This invention relates to a combined speed sensor and control valve for a rotary fluid motor. The speed sensor and control valve may be incorporated with the rotary shaft of a rotary vane air motor to effect cutoff of air supply to the motor in the event the speed of the motor becomes excessive.
The use of governors for speed control of rotary vane air motors is well known. Additionally, speed sensor devices associated with the rotary shaft of an air motor, known as overspeed controls, are utilized to terminate air flow to air motors in the event that excessive speeds occur due to some failure in the governor.
Patents disclosing various methods for providing overspeed control for rotary vane air motors include U.S. Pat. No. 3,767,332. That patent discloses positioning of weights on opposite sides of a rotating output shaft of an air motor. At rotational speeds below a pre-selected level the weights remain positioned tightly against the shaft. When the rotational speed of the shaft exceeds a preselected level, the weights are drawn radially outwardly due to the centrifugal force. As the weights swing outwardly, they engage a trigger mechanism which, in turn, operates a mechanical linkage to terminate a supply of air to the air motor. U.S. Pat. No. 2,586,968 and U.S. Pat. No. 3,591,372 disclose similar mechanisms.
U.S. Pat. No. 3,749,530 discloses yet another approach utilizing the centrifugal force associated with the rotating shaft of an air motor. In U.S. Pat. No. 3,749,530, a bellville spring is deflected by centrifugal force to a position which will close air inlet passages in the event of excessive speed of the output shaft of the air motor. U.S. Pat. No. 2,973,771 and U.S. Pat. No. 1,384,113 are of a similar nature. U.S. Pat. No. 4,298,317 appears to combine features of U.S. Pat. No. 3,749,530 and U.S. Pat. No. 3,071,115 discussed below.
U.S. Pat. No. 4,184,819 discloses yet another overspeed control mechanism wherein a member may be displaced from a latched position by centrifugal force to close a shutter for the air supply to the air motor. U.S. Pat. No. 4,278,103 discloses an overspeed control wherein a split ring is released from a cage upon excessive speed of a rotary shaft. The split ring then moves to block air inlet passages to the air motor.
U.S. Pat. No. 3,071,115 discloses an overspeed control device for an air motor wherein weights on opposite sides of a rotating shaft move in response to excessive centrifugal force and release a closure member which acts to close the air inlet to the rotary vane air motor.
The reference patents disclose speed sensor and speed control devices that provide adequate overspeed safety control. However, a device of simpler construction with fewer parts that is less expensive to manufacture, easy to service and sensitive to various speed settings is a desirable product.